Since the PM parts yield is based on set conditions (for example, Pro C5200S/C5210S: A4LEF, 26P/J, FC70%, etc), if a machine is used in an unexpected manner, parts could reach their life before the prescribed yield (EM), or could exceed the prescribed yield.
However, if the machine uses the running distance of the parts (which is a calculation based on the total number of revolutions made by the parts), PM can be carried out at more precise times, because the running distance reflects the actual status of the machine.